Many patients benefit from receiving therapeutic gas (e.g., nitric oxide gas) in inspiratory breathing gas flow from a breathing circuit affiliated with a ventilator. The ventilator can be, for example, a constant flow ventilator, variable flow ventilator, high frequency ventilator, bi-level positive airway pressure ventilator or BiPAP ventilator, etc.). To provide therapeutic gas to the patient, the therapeutic gas may be injected into the inspiratory breathing gas flowing in the breathing circuit. This inhaled therapeutic gas is often provided via a therapeutic gas delivery system as a constant concentration, which is provided based on proportional delivery of the therapeutic gas to the breathing gas. Further, a sampling system (e.g., affiliated with the therapeutic gas delivery system) may continuously draw in the inspiratory breathing gas flow to at least confirm that the desired dose of the therapeutic gas in the inspiratory breathing gas flow is being delivered to the patient. For example, a sample pump may pull in inspiratory flow (e.g., in the vicinity of the patient) to confirm that the desired therapeutic gas concentration is in fact being delivered to the patient in need thereof.
One such therapeutic gas is inhaled nitric oxide (iNO). In many instances iNO is used as a therapeutic gas to produce vasodilatory effect on patients. When inhaled, NO acts to dilate blood vessels in the lungs, improving oxygenation of the blood and reducing pulmonary hypertension. Because of this, nitric oxide is provided in inspiratory breathing gases for patients with various pulmonary pathologies including hypoxic respiratory failure (HRF) and persistent pulmonary hypertension (PPH). The actual administration of iNO is generally carried out by its introduction into the patient as a gas along with other normal inhalation gases, for example, by introducing iNO, from an iNO delivery system, into the inspiratory flow of a patient breathing circuit affiliated with a ventilator.
Separately and/or in conjunction with iNO, patients may receive inspiratory breathing gas flow containing liquid particles (e.g., moisture from humidified air, etc.) and/or other particles. Although this matter in the inspiratory breathing flow may provide additional benefit to the patient, it may interfere with or degrade operation of the sample gas analyzer. For example, the sample gas analyzer itself may work best when it receives sample gas within a given humidity range, and liquid particles as described above may be inconsistent with that range.
One known technique directed at keeping the sample gas at a desired humidity is to use, as part of the pathway of the sample gas before it arrives at the analyzer, a tubing formed of a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, for example, the commercially available Nafion® tubing. Properties of such tubing include a permeability that is very selective to water and that provides rapid transfer through the tubing walls. Provided that the permeability is maintained, such tubing can provide a mechanism operating as follows: if the humidity level of the sample gas passing through the tubing exceeds an acceptable maximum (and assumedly above ambient), some of that excess humidity will permeate out through the tube walls before the sample gas reaches the analyzer. Conversely, if the humidity level of the sample gas passing through the tubing is below the acceptable minimum (and assumedly below ambient), some of the ambient humidity will permeate in through the tube walls and raise the humidity of the sample gas to be within an acceptable range, prior to reaching the analyzer.
However, a conventional arrangement of Nafion tubing can form, over time, a dry external layer, i.e., at its outer wall surface, or dry inner layer at its passage wall surfaces, or both. With subscribing to any particular scientific theory, the inventor believes the mechanism of the drying may be a dehydration of the aqueous sulfonic acid inherent to the Nafion construction. Such dry layers can effectively become an obstruction to the above-described humidity conditioning function. This drying and obstructing layer formation can significantly shorten the operational life of Nafion (and equivalent) tubing type humidity conditioners.
Accordingly, there is a need for a humidity conditioner having the performance that can be obtained with Nafion and, concurrently, a significantly longer operational life than provided by conventional technique Nafion humidity conditioners.